1. Technical Field
The invention relates a new method for to the preparation of quinolinic carboxylic acids and derivatives thereof.
2. Background
Heterocyclic compounds of the quinolinic acids are known from the literature. They are intermediates for a broad class of compounds known as quinolones which have antibacterial activity. These compounds were prepared in the late 1930's and the early 1940's by the method of R. G. Gould and W. A. Jacobs, J. Amer. Chem. Soc. 61,2890 (1939). The method consists of the cyclization of diethyl anilinomethylenemalonate derivatives in Dowtherm A, diphenylether at temperatures of 250.degree.-300.degree. C. The starting materials for the cyclization reaction are prepared from a substituted aniline and diethyl ethoxymethylenemalonate. This method has been employed in a number of syntheses, 4,7-Dichloroquinoline, J. Amer. Chem. Soc. 68, 113 (1946); J. Amer. Chem. Soc. 68, 1204 (1946). 6,7 or 8 halo-4-hydroxyquinoline is described in J. Med. Chemistry 21,268 (1978). Other high boiling solvents have been utilized in this reaction as described in German Offenlegungsschrift Nos. 2,343,462 and 2,441,747, U.S. Pat. Nos. 3,149,104 and 3,673,193 and J. Heterocyclic Chem. 21,673 (1984). The use of polyphosphoric acid, sulfuric and acetic acid has been described in J. Org. Chem. Soc. 32, 4155 (1967) and 33, 1218 (1968) and J. Heterocyclic Chem. 27, 1527 (1990). In Pharmaceutical Industry 1986, 17 (9) 390-394, the ring closure of the anilinomethylenemalonate derivative is carried out with various Lewis Acid catalysts namely polyphosphoric ester, polyphosphoric acid, phosphorousoxychloride, phosphorous pentoxide, and a mixture of acetic anhydride and sulfuric acid. The yields obtained with these prior art methods are generally inferior to those of this invention.
A variation on this reaction is the use of anilinomethylenemeldrum's acid esters in place of the normal anilinomethylenemalonic acid esters. These materials are more reactive. However, they are much more expensive to make. Examples of the use of these compounds are given in G. B. Patent 1,147,760; J. Prakt. Chemie. 333, 267 (1990) and J. Heterocyclic Chem. 27, 1527 (1990).
Chloroquine is a quinoline derivative that was found safe for the treatment of plasmodium falciparum malaria in 1946. It was prepared from m-chloroaniline and ethyloxalacetate. The resultant m-chloroanilinomaleate or fumarate derivative was cyclized in diphenylether at high temperature. An industrial procedure is described in Ind. & Eng. Chem (41), 4, 1949, 654-662.
It is advantageous to have a method of preparation that does not utilize Dowtherm A, diphenylether. It is a suspect carcinogen and toxic. High boiling solvents are difficult to separate from the product and generally washing with a low boiling solvent is required to remove the high boiling solvent. In some cases, the addition of a low boiling hydrocarbon solvent is also necessary to precipitate the product from the diphenyl-ether reaction solvent. This situation creates further problems. It is more difficult to recycle the solvent under these conditions. It is advantageous to carry out the reaction in a solvent that can be diluted with water and disposed of without presenting an environmental hazard. It is also an advantage to use inexpensive, readily available starting materials. These and other advantages are achieved by the invention.
Although polyphosphoric, sulfuric, and acetic acid have been found to be effective reaction solvents for the cyclization of certain halogen substituted anilinomethylenemalonates as noted above, they do not provide satisfactory results in the cyclization of trifluoroanilinoacrylic acid esters. The present invention provides an efficient process for preparation of quinolinic acids in high yield by the cyclization of anilinoacrylic acid esters selected from anilinomethylenemalonate, anilinofumurate and anilinomaleate including the trifluoro-substituted derivatives thereof at a moderate temperature without the use of environmentally dangerous, toxic solvents.